Fabrication of soft plastic contact lens blank and composition therefor

ABSTRACT

GRAFT OR BLOCK COPOLYMERS OF HYDROXY ALKYL METHACRYLATE ESTERS AND POLYVINYL PYRROLIDONE ARE (1) CAST IN A SHAPING MOLD AS A MONOMER-POLYMER DISPERSION, POLYMERIZED TO A SOLID AT 40-60*C. IN THE PRESENCE OF LOW AND MEDIUM TEMPERATURE FREE RADICAL INITIATORS, (2) THE SOLID TAKEN OUT OF THE MOLD AND HEATED TO 90-120* C., AND THEN POST-POLYMERIZED BY (3) RADIATION WHILE DRY AND BY (4) HYDROGEN PEROXIDE TREATMENT TO FORM HYGROSCOPIC, SOILD, SHAPED MASSES WHICH MAY BE CUT IN THE DRY STATE, AFTER STEP (1), INTO CONTACT LENSES. THE LENSES MAY BE EQUILIBRATED IN THE WET STATE BY HYDRATING WITH NORMAL SALINE SOLUTION. THE LENSES MAY BE MAINTAINED BY TREATMENT WITH HYDROGEN PEROXIDE. STEPS (3) AND (4) TOUGHEN THE LENS, INCREASE ITS ELASTICALLY AND ITS ELASTIC RECOVERY AND IMPROVE ITS DIMENSIONAL STABILTIY. FROM 2045% BY WEIGHT OF POLYVINYL PYRROLIDONE IMPARTS HYGROSCOPIC AND UNUSUAL WATER-SWELLING CHARACTERISTICS. THE WATER SWOLLEN LENS CONTAINS FROM 40, 80% WATER PREFERABLY FROM 50-55%, AND IN ISOTONIC SALINE, THE WATER CONTENT CHANGES TO ABOUT 52-58%. AS A RESULT OF THE POLY-   VINYL PYRROLIDONE INCORPORATION, THE LENS IS READILY CLEANED AFTER USE IN THE EYE WITH DILUTE HYDROGEN PEROXIDE TO RID IT OF IMBIBED MUCO-PROTEIN, CATALASE AND THE LIKE.

July 2, 1974 K. F. O'DRITSCOLL ET AL FABRICATION OF SOFT PLASTIC CONTACTLENS BLANK FORM ,1-

SLURRY CAST ON TE F LON HYDROXY ALKYL METHACRYLATE andPOLYVINYL'PYRROLIDONE LOW TEMPERATURE INITIATOR MEDIUM TEMPERATUREINITIATOR FIRST STAGE CURING LOW TEMP. (40 C.)

MEDIUM TEMP. (105-115 C.)

CUT TO CURVATURE AND POLISH (FIG. 4a-4dl AND COMPOSITION THEREFOROriginal Filed Nov. 30, 1969 3 Sheets-Sheet l STIR and DE-GAS REMOVEFROM CASTING 2- SECOND STAGE R G FORM AND PLACE CYLINDER ON TRAY FORREMOVAL BY ARBOR PRESS (FIG. 5)

3 2, 1974 K F.o'DR|sco| L ETAL 3,822,196

FABRICATION SOFT PLASTIC CONTACT LENS BLANK AND COMPOSITION THEROrlglnal Flled Nov. 50, 1969 EFOR 3 Sheets-Sheet 2 RADIATION HYDRATIONAND I ALKALINE SWELLING I (SOFTENS LENS) i I 1% SODIUM BICARBONATE IDISSOLVED IN WATER at pH 8 for 2 20 hours OSMOTIC SWELLING TO MATCHSALINITY I 0.7 0.9% NaCl SOLUTION HEAT TO 200F for 4 12 hours WITH ATLEAST 3 CHANGES of SOLUTIOfl I v 3% HYDROGEN PEROXIDE IN WATER I at pH 9and 0.6 0.9% SALINE for Q hour! EOUILIBRATION AND WASHING OUT PRODUCTSOF OXIDATION NORMAL SALINE (0.9% NaCl, BUFFER 3 4% NaHCO3. pH 11 12) y1974 K. F.O'DRISCOLL ETAL 3,822,16

FABRICATION OF SOFT PLASTIC CONTACT LENS BLANK AND COMPOSITION THEREFOROriginal Filed Nov. 30, 1969 3 Sheets-Sheet 5 United StatesPatentOfl-ice 3,822,196 FABRICATION OF SOFT PLASTIC CONTACT LENS BLANKAND COMPOSITION THEREFOR Kenneth F. ODriscoll, Williamsville, and AllanA. Isen, Buffalo, N.Y., assignors to Warner-Lambert Company, MorrisPlains, NJ.

Original application Nov. 30, 1969, Ser. No. 880,828, now Patent No.3,700,761. Divided and this application Aug. 25, 1972, Ser. No. 283,735

Int. Cl. B01j 1/10; 008d 1/22; C081 33/04 U.S. Cl. 204-15916 2 ClaimsABSTRACT OF THE DISCLOSURE Graft or block copolymers of hydroxy alkylmethacrylate esters and polyvinyl pyrrolidone are (1) cast in a shapingmold as a monomer-polymer dispersion, polymerized to a solid at 40-60 C.in the presence of low and medium temperature free radical initiators,(2) the solid taken out of the mold and heated to 90-120 0, and thenpost-polymerized by (3) radiation while dry and by (4) hydrogen peroxidetreatment to form hygroscopic, solid, shaped masses which may be cut inthe dry state, after step (1), into contact lenses. The lenses may beequilibrated in the wet state by hydrating with normal saline solution.The lenses may be maintained by treatment with hydrogen peroxide. Steps(3) and (4) toughen the lens, increase its elasticity and its elasticrecovery and improve its dimensional stability. From 20- 45% by weightof polyvinyl pyrrolidone imparts hygroscopic and unusual Water-swellingcharacteristics. The Water-swollen lens contains from 40-80% Water,preferably from 50-55%, and in isotonic saline, the Water contentchanges to about 52-58%. As a result of the polyvinyl pyrrolidoneincorporation, the lens is readily cleaned after use in the eye withdilute hydrogen peroxide to rid it of imbibed muco-protein, catalase andthe like.

This is a division of application Ser. No. 880,828, filed Nov. 30,1969', now U.S. Pat. No. 3,700,761.

BACKGROUND OF THE INVENTION (1) Field of the invention The inventionrelates to a method of shaping and polymerizing, at low (40-60" C.) andmedium temperatures (90-120" 0.), a monomer-polymer dispersion bycasting in a mold and continuing the polymerization after removal fromthe mold, the dispersion consisting preferably of 20-45% of polymerizedvinyl pyrrolidone and 80-55% of monomethacrylate ester of a glycolselected from the group consisting of ethylene glycol, propylene glycol,diethylene glycol and dipropylene glycol, there being present no morethan about 1% by weight of methacrylic acid and no more than 0.2% byweight of the dimethacrylate of the aforesaid glycols. Amounts ofimpurities in excess of these limits cause haze or cloudiness in theproduct, undue hardness of the casting after hydration, and lessen theamount of water which is absorbed by the hygroscopic solid polymerizedproduct. The monomer is essentially pure hydroxy alkyl methacrylateester.

An essential feature of the method of the present invention is thestagewise post-polymerization of the bulk polymerized solid castingafter free radical initiation at low (4060 C.) and medium (90120 C.)temperatures by means of (a) polymerizing radiation of the dry solid,and (b) hydrogen peroxide treatment of the waterswollen product in anisotonic salt solution toughens the solid post-polymerized product intocompletely hydrated condition (swollen with from 45-80% water) which isproportional to the polyvinyl pyrrolidone content.

3,822,196 Patented July 2, 1974 (2) Description of the prior art FieldsU.S. Pat. 2,136,422 shows the bulk polymerization of ethylene glycolmonomethacrylate with free radical initiator such as benzoyl peroxide atelevated temperatures in order to obtain a completely transparent, solidproduct which is cut and turned on a lathe to make a furniture leg orthe like.

Armen et al. U.S. Pat. 3,086,956, in Example 7, shows polymerization ofpolyglycol monomethacrylate with polyvinyl pyrrolidone and ammoniumpersulfate initiator at pH 5 in the presence of water to provide a graftcopolymer in the form of a turbid aqueous solution containing 19.7%solids.

Ackerman et al. U.S. Pat. 2,923,692 shows lightly crosslinked copolymersof esters of methacrylic acid and vinyl pyrrolidone (see column 7, line32). The products of Ackerman et al. contain highly water-sensitive,crosslinked acrylic acid groups which can be neutralized with alkali toform a smooth, non-grainy mucilage after the product has been purifiedby washing, dried and then ground in a homogenizer or colloid mill.

The bulk polymerized ester of Fields, neutralized, hydrated, washed andgrbund by the method of Ackerman et al., would be expected to give amucilage or glue. It has been found that before grinding, the producthas limited hydration capacity (maximum of 20-30%) even with substantialamounts of acrylic or methacrylic acid being present in the interpolymeror copolymer. Commercial soft hydrophflic lenses made under theTrademark So-fiens, described in U.S. Pat. 3,408,429, are discussed morefully below.

Robinson U.S. Pat. 2,941,980 shows water-soluble polymers and copolymersof pyrrolidone with various monomers, such as acrylic acid, vinylacetate and the like, and these water-soluble polymers are mixed withalkylated phenols serving as plasticizers to provide coatings for basesof metal, paper, glass, etc., to afford protection against water.

The accelerating effect of up to 1% of vinyl pyrrolidone on thepolymerization of methacrylate esters is taught by Munday et al. U.S.Pat. 3,232,912, but the polymerized products which are produced areliquids or low-melting solids, useful as detergents in lubricating oilsor as sludge dispersants in heating oils.

Copolymers of vinyl pyrrolidone and acrylic acid, as in Robinson, orgraft polymers of polyglycol methacrylate with polyvinyl pyrrolidone, asin Armen et al., are not satisfactory as water-swollen, tough contactlens blanks. These products form low-strength films which, when wet withWater, are easily distorted by tensile forces and exhibit poor recovery,inadequate elongation and inadequate toughness.

One would not expect that graft polymers in proportions taught byAckerman et al., Armen et al., Robinson or Munday et al. might be usefulto form tough, transparent, water-swollen contact lenses, capable ofbeing sterilized and cleaned with hydrogen peroxide.

SUMMARY OF THE INVENTION In general, the method converts a free radicalinitiated solid polymer containing polyvinyl pyrrolidone and polyhydroxyalkyl methacrylate to a highly permeable, soft, hydrated, shaped masshaving improved toughness, elasticity and recovery by treating the drysolid mass with radiation to aid densification and thereafter hydratingthe mass in saline solution and treating with hydrogen peroxide to causefurther toughening by chemical interaction between the polyvinylpyrrolidone and polymerized methacrylate.

In a preferred form, a tough, soft, hydrated, fluidpermeable contactlens cut from a hard blank is prepared by casting a compositionconsisting essentially of 20-45% of solid, high molecular weightpolyvinyl pyrrolidone in a network of 80-55% of hydroxyethylmethacrylate, hydroxy propylmethacrylate, or diethylene glycolmonomethacrylate which may contain, as impurities, less than 1% ofmethacrylic acid, preferably not more than 0.2%, and up to 0.2% ofethylene glycol dimethacrylate. The polymerization of the bulk matrixand preformed polymer is carried out in stages, first in a casting moldand then outside of the mold, as follows:

(1) In the open cylindrical casting mold with a lowtemperature peroxide,such as acetyl peroxide, di-secondary butyl peroxy dicarbonate,cyclohexanone peroxide, etc., at 40-60" C. for a period of 4-24 hours;

(2) Out of the mold with a medium-temperature, free radical initiator,such as benzoyl peroxide, diethyl peroxide, azoisobutyronitrile,orthotolyl peroxide, etc., at a temperature of 90-120 C. for a period of/2 to 2 hours;

(3) Out of the mold as a shaped, hard, polymerized mass with actinic orhigh energy radiation, such as ultraviolet radiation, gamma radiation,etc., after the lens has been cut to size; and,

(4) Finally with hydrogen peroxide in hydrated condition and in thepresence of salt which produces the osmotic equivalent of normal salinesolution, whereby the cut, water-swollen lens, containing from 40-80%water, preferably 50-60% water, is toughened in the wet condition.

Step (3) increases the toughness of the lens in hydrated condition, asmeasured by a bubble bursting test, which blows compressed air againstthe lens to break or burst it and step (4) further increases thetoughness of the waterswollen lens and acids in cleaning the lens ofdebris which accumulates thereon from the eye.

It was completely unexpected to find that a low methacrylic acid mediumwill provide a graft of hydroxy ethylmethacrylate which is formed withpolyvinyl pyrrolidone and thereby provide castings from these materialsin bulk which are tough, dimensionally stable and uniformly reproduciblein hydrated, swollen form to contain from above 40% and preferably50-60% water in which the permeability of the hydrated product has beenincreased by post-polymerization treatment, first with radiation whendry and then with hydrogen peroxide in isotonic salt solution.

The function of polyvinyl pyrrolidone in responding to hydrogen peroxidetreatment which, in the preferred embodiment of the invention, has aFikentscher K value of from 30 to 90, appears to be a critical aspect ofthe new and unexpected properties of toughness, elastic recovery andelasticity developed by the graft copolymer with hydroxy alkyl acrylate.

Polyvinyl pyrrolidone is comparable to gelatin and albumen in respect toits high atfinity for water and its low toxicity and general biochemicalinertness. The polyvinyl pyrrolidone which is preferred for the presentcontact lens manufacture has a Fikentscher K value of 33, correspondingto a molecular weight between about 25,000 and 50,000, the numberaverage molecular Weight by osmosis being about 37,000 which is abouthalf of that of bovine serum albumen. The carbonamide groups present ingelatin are responsible for thread-like structures in the hydration ofgelatin emulsions which have been detected under the ultramicroscope ingrainless photographic emulsions containing from 5-10% of gelatin insolutions adjusted to the isoelectric point. Surprisingly, electronmicroscope photographs of the hydrogen peroxide-treated lens structureof the present invention show no threads. Polyvinyl pyrrolidone impartshygroscopic characteristics to the product, is distributed in the matrixand takes part in chemical interaction with hydrogen peroxide. Thereappears to be increased permeability and diffusibility of solutes inwater through the polymer membrane. This polymer membrane, used as acontact lens,

can be cleaned with hydrogen peroxide to remove catalase deposited fromtears and organic debris which tend to accumulate in the Wichterlehydrophilic contact lenses.

The hydrogen peroxide has the effect of clearing the lens of anycatalase or of any other muco-protein of the eye. At the same time, itincreases the strength at a slow rate without affecting the fiuidpermeability which is so important to the performance. This is over andabove the initial toughening of the product which is achieved by thefirst wash in hydrogen peroxide. The use of the peroxide, therefore,becomes a maintenance procedure which not only sterilizes the lenses butmaintains clarity, transparency and fluid permeability.

Accordingly, this treatment permits freedom from eye irritation andprevents the development of edema under the lens when the lens is worncontinuously for 24 hours and longer.

The hydrated hydrogen peroxide-treated product of the present inventionappears to possess significantly different properties from gelatin inits resistance to change by acids, alkalis and relatively hightemperatures in the wet condition. Gelatin, being amphoteric, reactswith acid and alkali and reversibly dissolves on heating unless it isdenatured and fiocculated by overheating when wet. In contrast, thepresent product withstands boiling water for periods up to 72 hourswithout alteration of its desirable permeable characteristics. Althoughthe chemical mechanism of alteration of carbonamide linkages byradiation and hydrogen peroxide polymerization is not fully understood,it is clear that a critical and significant enhancement of physicalproperties has been achieved and this could not be obtained by any othermethod.

BRIEF DESCRIPTION OF THE DRAWING In the fabrication of a soft,water-swollen, plastic contact lens from a hard, dry blank by thepreferred method of the invention, a simple casting apparatus is usedfor shaping the blank and for polymerizing the blank which isillustrated in the attached drawing, in which:

FIG. 1 is a flow diagram showing mixing of ingredients, stirring,degassing, pouring into the mold and placing the filled mold into theoven for the first and second stage curings at low and mediumtemperatures, respectively, to produce a hard, transparent, shaped masswhich is cut and polished;

FIG. 2 is a diagrammatic view showing the placement of male and femalemold parts to shape the hard, transparent solid which is subsequentlycut;

FIG. 3 is a flow diagram showing the manufacturing steps taken in aparticularly preferred embodiment whereby radiation treatment,water-swelling in alkaline medium, osmotic swelling and hydrogenperoxide hardening are carried out to improve the physical propertiesand water permeability and to diminish osmotic swelling of the cut andpolished lens;

FIGS. 4a, 4b, 4c and 4d show stages in the cutting of the shaped massejected from the mold in FIG. 2 in achieving the finished lens; and,

FIG. 5 is a sectional view which shows the relation of the mold partsand the hard, transparent, shaped mass after one-stage curing and beforeejection from the mold.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 To parts of distilledhydroxyethylmethacrylate containing up to .2% of ethylene glycoldimethacrylate and less than 1% of methacrylic acid as impurities wereadded 40 parts of powdered polyvinyl pyrrolidone (Plasdone C Grade,supplied by GAF Corporation) having a Fikentscher K value of 33, numbermolecular weight of 37,000, molecular weight range of 25,000-50,000 withthe upper 15% of K value distribution being 39% by weight of the polymerand the lower 25% of K value distribution being 18.5%. This polymer,hereinafter termed PVP, is hygroscopic and had a moisture content ofabout 3%, but picked up 1 or 2% additional moisture from the atmospherein the plant.

A 40 part portion of the liquid methacrylate, hereinafter termed HEMA,was mixed with catalyst, e.g. 0.2 grams of benzoyl peroxide in powderedform and 0.2 grams of di-secondary butyl peroxy dicarbonate, availableunder the trade named of Lupersol 225 from Lucidol Chemical Corporation,Buffalo, NY.

The catalyst-liquid mixture, 40 parts, was added to the PVP-HEMAmixture, 120 parts, and was mixed carefully to provide 160 parts ofmonomer with 40 parts of polymer dispersion or slurry. These proportionscut down the shrinkage as compared with liquid HEMA alone. The amount ofsecondary butyl peroxy dicarbonate catalyst which is particularlyeffective at a temperature of 40'-60 C. and of benzoyl peroxide catalystwhich is particularly effective at a temperature of 90120 C. is .2 partof each catalyst per 200 parts of liquid PVP mixture containing 160parts of liquid monomer and 40 parts of PVP, e.g. a proportion of about0.1% for each of these catalysts. PVP was present in an amount of 20% byweight of the dispersion. The dispersion was de-aerated to permit airbubbles to escape, and the mold was filled in the manner showndiagrammatically in FIG. 1. The tray of molds was then placed in an aircirculating oven for 20 hours at a temperature of 40 C. At the end ofthis time, the molds were removed from the oven and taken apart by usinga small arbor press against the flat end of the Teflon core at thebottom of the mold unit. This forced the cast blank out of the other endof the sleeve. The cast blanks were placed on aluminum sheets andreturned to the oven where they were post-cured at a temperature of 110C. for 1 /2 hours. When the trays were removed from the oven, thefinished cast plastic blanks were a polymer consisting of PVP to whichpoly-HEMA had been grafted.

Example 2 The casting procedure set out in Example 1 was carried out,but instead of using 20% by weight of PVP, 30% by weight was used. Thelens made by the technique of Example 1 contained about 55% of water asmeasured in isotonic saline and resulted in a lens that came up to theexacting standards set for Example 1.

Example 3 The process of Example 1 was repeated, except that diethyleneglycol monomethacrylate was used with 25% by weight of PVP. This lens,too, met the standards set in Example 1.

Example 4 The process of Example 1 was repeated except that instead of20% of PVP, 35% by weight was used. The resulting lens came up to thestandards set for Example 1.

Example 5 A mixture of 80 parts of hydroxy propyl methacrylate and 80parts of HEMA was used for the monomer phase with 20% by weight of PVPand the process of Example 1 was repeated. The resulting lens came up tothe high standards set for Example 1.

The water content of the lens made and tested in Example 1 was about 51%in water and about 49.5% in 0.9% saline solution. In contrast, the watercontent of poly-HEMA from which PVP has been excluded is about 38% and36%. The water content of the remaining examples was substantially thesame as that in Example 1. Generally, the main differences imparted bysubstituting propylene glycol monomethacrylate or diethylene glycolmonomethacrylate is to lower the refractive index and to make thepolymerized solid slightly more flexible.

If, in the foregoing examples, PVP is used in an amount less than 20%,the water uptake value of about 50-60% is not achieved in the hydratedwater-swollen 6 polymerized mass and the desired toughening and increasein strength are not achieved by subsequent hydrogen peroxide treatment.

If the low temperature initiator is omitted and polymerization iscarried out at 90-l20 C. for /2 to 2 hours, the solid product is notuniform in physical properties nor does it provide the toughening andimproved strength necessary to come up to the desired standard. Withoutboth low and medium temperature initiators, the improvement inpermeability over the commercial Sofiens made under the Wichterlepatents is not achieved, nor is consistent reproducibility possible.

Accordingly, the critical two-stage initiation at temperatures of 4060C. in the mold to form the solid rod and at 90-l20 C. out of the mold,in a tray in an oven, to harden the self-sustaining rod provides a rodof stock material of Shore A Hardness value between 70 and 90. which canbe cut and polished into lenses by the familiar technique used with hardacrylic material. Even without further treatment, such lenses can behydrated and waterswollen to surpass the performance of the presentlycommercially available hydrophilic lenses.

If more than 45% of PVP is used in the polymerized mass, the mass afterhydration becomes excessively soft. Even after post-polymerization, theproduct cannot be toughened to match the high strength and elasticityvalues of the preferred examples above. Only in the range of 2045% PVPcan the present polymerized composition, free from cross-linker, matchthe strength properties of the commercial Soflens. The Soflens materialdoes not possess the same high permeability rate of diffusion which inthe present examples is from 10-15 times that of the Soflens material.

MANUFACTURING THE LENS FROM THE BLANK The manufacture of contact lensesin the hard state and the further processing of the lenses aftercompletion and hydration to the soft state are disclosed and claimed inthe copending application of Allan A. Isen, entitled Method of CuttingHydrogen Peroxide-Treated Soft Contact Lens and New Lens Made Therefrom.

The lenses are made by cutting and polishing the shaped masses in thehard state, as shown in the flow diagram of FIG. 1 and in the views ofFIGS. 2, 4a-4d, and 5, so :hat they appear to be exactly like a hardacrylic contact ens.

The molding ingredients, comprising the mixture of hydroxy alkylmethacrylate, PVP, low and medium temperature initiators, cure in thefirst stage in the molds and in the second stage in the trays to producehard, transparent, shaped, plano-concave cylinders 20, as illustrated inFIG. 2. The concave surface is formed by male mold member 10 fittinginto female mold member 11. The interior surface of the female member 11is coated with Teflon, as is the outer surface of the male member 10.After curing, the Shore A Hardness value of the shaped mass 20 isbetween about and 90. Subsequent post-polymerization treatment increasesthe Shore A Hardness value by from 3 to 10 points. At higher PVPconcentrations, lower initial Shore A Hardness values are obtained.Subsequent treatment, e.g., post-polymerization, by radiation causes agreater increase in Shore A Hardness at these higher PVP concentrationsand this demonstrates that radiation is especially effective inpost-polymerization of the PVP moiety in the product. Radiation alsotends to cause slight embrittlement so that it is easier to cut theentire mass 20 before radiation treatment.

Because of the PVP content in the lens and the two stages of curing,there is no trace of unreacted material in the cast blank 20, and cutlenses which are formed by the steps shown in FIGS. 4a-4d havewater-swelling characteristics far beyond the commercial hydrophiliclenses available in the prior art. The commercial Soflens, from theBausch & Lomb Company, has a water uptake of 38% in comparison with a5055% water uptake for the cut lens of FIG. 4 herein, prior to radiationand 7 hydrogen peroxide treatment. This combination of high hardness inthe dry state and high water uptake in the wet state of the present lensblank material permits an entirely different and simpler manufacturingprocess to be carried out than with the Wichterle lens which must be cutwhen mounted on a support, as described in US. Pat. 3,361,858. Thepresent material contains no cross-linker as is required in the lenscomposition of this patent and it is surprising that the substantiallypure poly-HEMA matrix of the present invention, having a Shore AHardness value close to 90, can be easily cut in the dry state to verysmall tolerances of about M mm. and thereafter can be hydrated to imbibeat least 50% more water than the prior art lens. This cutting in the drystate permits thinner edge sections to be produced and permitsuniformity in lens manufacture which cannot be achieved in the prior artmanufacturing methods.

In the hard state, the index of refraction of the cast blank 20 isapproximately 1.49. In the hydrated state, the index of refraction ofthe lens is approximately 1.39 to 1.40. The lenses become larger,thicker and flatter when they are changed to the soft state byhydration. In the cutting and polishing processing of the lenses, anadditional reversal in shape occurs and they become somewhat steeper andslightly smaller in diameter. All of these changes are taken intoaccount to produce the desired specifications of curvature and dimensionin the hydrated state.

The lens blank 20 is a small cylinder with a concave curve at one endwhich must be optically finished and a small amount of stock is removedfrom this surface, e.g. a minimum amount of about .2 mm. in thicknessand a maximum of .5 mm., the removal being symmetrical and from theentire surface.

The following are the steps in manufacturing after the low temperatureand medium temperature cures of the blank 20. After the low temperaturecure, the blank 20 is removed in the manner shown in FIG. wherein ram 13pushes against the planar surface of the blank to eject the blank fromthe female mold member 10. The blank is removed from the same end intowhich the dispersion or slurry was poured and this removal is completelydifferent from that which is carried out in US. Pat. 3,361,858, whereinthe lens is molded to size on a mount and is removed from the mount byimmersing in water to swell it and allow it to be peeled from the mount.After this, the blank of the present invention is cured in the mediumtemperature stage on trays and the steps below are followed:

Step 1Cutting The cutting steps are shown diagrammatically in FIGS.4a-4d. The dotted lines in FIG. 4a show removal of peripheral or radialportions of the blank in order to cut the 180 are down to about 120, asshown in FIG. 4a and in FIG. 4b. The planar surface is then out alongthe dotted line shown at the bottom of FIG. 4b in order to facilitatemounting the blank on a lathe, and this blank is shown in FIG. 40. Wherethe chuck of the lathe can handle the form shown in FIG. 4b, the planarcut shown in FIG. 4c is not required. The concave cut is made along thedotted line shown in FIG. 40 and the cut lens is shown in FIG. 4d.

In the lens made in accordance with the present invention, the flatsurface on the back of the blank is faced off in the manner shown inFIGS. 4b and 4c and the center of the flat surface is tapped to make apivot depression on a small jeweler's lathe. The diameter of the blankwas reduced in a Levin lathe to a size .1 mm. larger than the desiredfinished lens size (see FIG. 4a). The radius cut on the concave surfacematched the surface.

Step 2-Polishing of inner or back surface The base curve blank was thenmounted on an optical polishing machine and it was polished against abrass lap coated with adhesive tape whose curve matched the base curveof the blank. In the polishing, the lens blank rocked back and forth onthe polishing lap, and spun at the same time. Two polishing cycles wereused. The first employed Snow Floss Compound, made by Johns-Manville,mixed with odorless kerosene to the consistency of a thick paste. Thisrough polish procedure was used for 3 minutes. The finish polish wasdone with U.S.P. Grade of Zinc Oxide, made by Merck Pharmaceuticals,mixed with Vaseline to form a paste. This cycle also lasted for 3minutes. When the curve was finished, it was measured with a radiuscopefor radius and quality to have a radius of curvature within plus orminus .04 mm. of the original lathe radius cut.

Step 3Radius cutting the outer or front surface The finished base curvewas now mounted onto a brass or plastic chuck preparatory to radiuscutting and polishing the front surface. This chuck has a finished,polished, convex surface which matches the base curve of the blank. Therear of the chuck fits into a collet of a small, high precision jewelerslathe made by Levin & Sons. The chuck was heated slightly, sufficientlyto melt some mounting wax on the surface of the chuck. The finished basecurve was pressed firmly onto this surface and was allowed to cool. Thechuck was then mounted in a Levin lathe and its front surface was radiuscut in two stages. In the first stage, rough cutting removed all of thestock. In the second stage, finish cutting produced a highly smoothradius cut and an exact center thickness. The thickness was measured bya regular plunger thickness gauge through the small diameter hole in thecenter of the chuck, which was also used for evaluating the optics asthe lens was being finished. The front surface was then polished on anoptical polishing machine. The chuck mounted on a vertical spindle androtated as a polishing lap coated with adhesive tape rocked back andforth over the surface, spinning at the same time. The polish used wasSnow Floss Compound mixed with odorless kerosene to the consistency ofthin paste. It required 3 minutes to complete the surface, and theoptical quality was judged by removing the chuck from the spindle andviewing the optics in a lensometer through the hole in the chuck.

Step 4Cutting the lenticular groove on minus lenses On minus lenses, itis necessary to thin the edge by adding a minus lenticular cut to theperipheral region of the front of the lens. This is done with a singleedge razor blade and polished with molefoam and the zinc oxide polishingsolution. The width of this front lenticular region should not be reaterthan /2 of the diameter of the lens.

Step 5Adding inside bevel and inspection The lens was then removed fromthe chuck by heating the bottom of the chuck until the wax softened andthe lens could be slid off the chuck easily, and was then cleaned in atest tube with xylene which was put into an ultrasonic cleaner.

The finishing of the lens included the addition of a small flat bevel tothe inside aspect of the edge approximately .3 mm. wide. This was put onby grinding against an emery sphere or a diamond impregnated lap, andpolishing against a matching felt lap. Following this, the edge wasrounded and polished against a polyurethane sponge saturated with thepolish mixture or zinc oxide and odorless kerosene. The lens was thenrecleaned in xylene in the ultrasonic cleaner. It was measured andinspected for base curve radius, optical value and quality, thicknessand surface scratches.

Step 6-Irradiation treatment as shown in FIG. 3

Irradiation is preferably carried out under an ultraviolet lamp whichprovides a high energy source in the spectral range of 2000 to 4000angstrom units, for at least V2 hour, preferably 2-4 hours. The burstingstrength is increased from 7 p.s.i. gauge to 10.5-11.0 p.s.i. gauge, anincrease of at least about 50% of the original value and the hydratedlens loses pracitcally none of its elasticity and rapid recovery. Incontrast, the commercial Sotlens, the lens of the prior art, does notimprove under irradiation in its bursting strength. Therefore, it isclear that the PVP component in the original composition, as well as theunique two-step polymerizing procedure, e.g. the low temperatureinitiation and the medium temperature initiation referred to in FIG. 1,coact in a new way with irradiation treatment in the solid polymerizedstate to produce this new and unexpected result.

Ultraviolet sources, such as the mercury vapor tube, a Xenon lamp, or acarbon arc tube, may be used.

Other irradiation sources which may be used are a cobalt 60 source whichemits gamma radiation, spent reactor elements from a uranium pile whichalso emit gamma radiation, or high energy ionizing radiation from acommercially available source, e.g. Radiation Dynamics, Long Island,N.Y. X-rays may be used at exposure dosages of roentgens for a period ofminutes to 1 hour. Gamma radiation dosage for post-polymerizationtreatment is preferably from about 5 to about 95 megarads for 5 minutesto 1 hour, All treatments by irradiation are carried out at roomtemperature.

In this irradiation treatment, as shown in FIG. 3, the hard finishedlens was placed under a pure ultraviolet light for a period of 3 /2hours. The light source was 6 from the lens. The unit was covered toprevent light loss and the polymerization of poly-HEMA and PVP wascompleted in 2 hours. The light source was a 250 watt Spectralineultraviolet lamp.

Step 7Neutralization, hydration and hydrogen peroxide treatment Thisstep accomplished the neutralization and hydration of the lenses. Lenseswere placed in a .8% saline bath mixed with sufiicient bicarbonate ofsoda to produce a pH of 8. They remained in this bath for 2-20 hours.Each lens was held by a small flo-thru basket made of polypropylene. Thelenses were then placed in a bath of normal saline at approximately 200F. for 1 hour. The bath was then changed to fresh normal saline for aperiod of 3 hours and then changed again for an additional 4 hours. Thisboiling was done in a pressure cooker to which a condensing column hadbeen added to prevent evaporation and to increase the concentration ofthe saline.

The lenses were then placed, for 4 hours, in a bath of 10 volume reagentgrade hydrogen peroxide (3% H 0 to which had been added sufficient puresodium chloride to produce the equivalent of a normal saline solution.This caused the lenses to shrink in size and become hypertonic.Following this, they were boiled in the pressure cooker in distilledwater for 2 hours and again in normal saline for 2 hours (see FIG. 3).

BURSTING STRENGTH OF THE LENS The post-polymerization steps (6) and (7),irradiation and hydrogen peroxide, illustrated in FIG. 3 of the drawing,contribute to significant strengthening and toughening of thewater-swollen lens and provide thereby advantages not available in anycommercial lens of the soft hy-drophilic type.

The hard cut lens resulting from the manufacturing operations shown inFIGS. 1 and 4a-4d can be tested for bursting strength by binding theedges about the opening of A" pipe and measuring the air pressurerequired to burst the lens which has been boiled in water for 4 hours tohydrate it. This test carried out with the cut lens of FIGS. 1 and 4a-4dof the invention showed a bursting strength of 7 p.s.i. gauge pressure.This cut lens, based on poly-HEMA matrix containing 20% PVP, matched thebursting strength (7 p.s.i. gauge) of the centrifugally cast Sofiens"containing dimethacrylate cross-linker, thereby showing unexpectedimprovement in the absence of crosslinker and at almost 50% higher watercontent (52% uptake in the present lens against 37% in the Soflens).

After irradiation and hydrogen peroxide treatment by the process of theinvention, the bursting strength by the above mentioned test isincreased from 1045-11 p.s.i. up to 16-17 p.s.i., an increase of atleast 250% based upon the original bursting strength and an increase ofabout 100% of the original value as compared with the 50% increaseachieved by irradiation.

This enhancement of strength by hydrogen peroxide is uniquely based uponthe PVP content since the commercial Soflens does not show suchenhancement in bursting strength. Uniquely, both the irradiation and thehydrogen peroxide treatments are essential if the maximum burstingstrength is to be achieved and if the other lens properties, e.g.controlled elongation in lateral and vertical dimensions inwater-swollen state, are to be maintained.

These other lens properties, in water-swollen state, will be moreclearly visualized in comparison with the shape and dimensions of thehard lens shown in FIG. 4d. Upon immersing the lens in water at pH 8after radiation (see Block 3, FIG. 3), the radius of curvature of thelens expands 26%, the core diameter expands 35%, and the thicknessexpands 23%. These values of anisotropic expansion do not change if thelens is immersed in saline (Block 4, FIG. 3). The water uptake isbetween 48 and 55%.

The hydrogen peroxide treatment accomplishes the most surprisingimprovements in the physical properties of the hydrated, water-swollenlens which facilitate maintenance and cleaning of the lens by thepatient. By this treatment, there is accomplished, as mentioned above,an increase in bursting strength after irradiation of 10.5-11 p.s.i. upto 16-17 p.s.i. gauge pressure. If alkaline bicarbonate solution (1%) atpH 8 is repeatedly applied to the lens, a slight softening occurs andthe bursting strength falls to about 12.5-13.5 p.s.i. This effect isreversed by immersion in 3% hydrogen peroxide to regain the 16-17 p.s.i.value. Repeated treatment with hydrogen peroxide interspersed withsoftening treatment by alkaline bicarbonate solution increases thebursting strength still further up to values of 19-20 p.s.i.

FLUID PERMEABILITY CHARACTERISTICS The fluid permeability of the lensesof Example 1 was studied and compared with the Bausch & Lomb Sofiens,made by the process of Wichterle US. Pat. 3,408,429.

Individual vials of sterile fluorescein solution were made up variousdisodium fluorescein concentrations in 0.1 M phosphate buffered salineat a pH of 7.4.

An objective slit lamp fluorophotometer measured fluoresceinconcentration in the lenses, in the interior segment of the eye, and inthe solution. The fluorophotometer consists of a light sensing devicebuilt into the eye piece of the lamp and measures the fluoresceinconcentration in an area 0.08 mm. across. The instrument is accurate towithin plus or minus 2%. The unknown is compared with a fresh, stable,standard fluorescein solution.

RESULTS OF IN VITRO STUDIESFULLY HYDRATED 1) Uptake Fully hydratedlenses were placed in solutions of various fluorescein concentrations,were rinsed briefly after the test time in saline and were then mountedon the end of a glass test tube for measurement of the fluoresceinconcentration in the lens.

The lenses themselves absorb less than 3% of the emitted light and donot interfere with the test by reason of light absorption. The volume ofthe soaking solution is large in comparison to the lens volume.

Lenses fiuoresced uniformly under the slit lamp after seconds of soakingin a fluorescein (5 1()- mg./ml.) solution. Three distinct zones wereobserved in the Softens lenses soaked for 30 minutes due to thefluorescein slowly diffusing to the interior of the lenses. The lensesof the present invention take up fluorescein quite rapidly; uptake iscomplete in about 2 hours. The Bausch & Lomb lenses (Soflens) take upfluorescein slowly and continue to do so for over 24 hours, reaching afinal concentration approximately 2.3 times that in the lenses of thepresent invention.

(2) Elution studies After a 24 hour presoaking of the lenses in 1Omg./ml. fluorescein solution, they were placed in 4 cc. of bufferedsaline and the time rate of change of fluorescein concentration in thelenses and the eluting solutions were measured. At the end of 1 hour,the lenses of the present invention had released 70% of the fluoresceininto solution, while the Sofiens lenses released 25%. Only after 8 hoursdid the Soflens lenses release 90% of the bound fluorescein.

After elution from each type of lens, it was determined that the Soflenslenses took up twice as much fluores cein as did the lenses of thepresent invention, on a weight basis.

The total uptake of fluorescein was linearly related to theconcentration of the soaking solution over a 4000-fold concentrationrange between 5 10 and mg./ml. The present lenses were air dried, placedin fluorescein solution and the uptake by the dried lenses wassubstantially identical to the fully hydrated lenses.

RESULTS OF IN VIVO STUDIES A young female who had worn both conventionaland hydrophilic lenses without difficulty was studied. On the first day,she wore a lens of the present invention in one eye and no lens in theother. A single drop of sterile 2% fluorescein was instilled in each eyeat 0, 2, 4, 6 and 11 hours. The corneal and anterior chamberconcentrations were measured at 2, 4, 6 and 24 hours, each time removingthe lens 10 minutes prior to measurement. One week later, the subjectwore the Bausch & Lomb Sofiens in one eye and a methyl methacrylateconventional hard lens in the other. Drops were instilled at 0, 2 and 4hours and measurements were made at 0, 2, 4 and 6 hours, at which timethe Bausch & Lomb lens was removed. The corneal and anterior chamberconcentrations of fluorescein are shown in Tables 1 and 2 below. Thecorneal and anterior chamber concentrations were higher with the lens ofthe present invention than with the other lenses. There was essentiallyno difference between using no lens, standard methacrylate lens, or theBausch & Lomb lens. At the end of 6 hours, the corneal and anteriorchamber concentrations of fluorescein in the eye with the lens of thepresent invention were 6 to 8 times that attained with any other mode oftreatment. Furthermore, the lens of the present invention was able tomaintain the fluorescein concentration in the ocular tissues for 24hours despite the known rapid exit of fluorescein from the eye. Itshould be noted that the lens had not been presoaked in fluoresceinprior to insertion.

In other studies, the present lenses were presoaked in solutions of 0.1%and 0.01% fluorescein and inserted into the right eyes of three rabbitsAt the same time, a drop of the 0.01% solution was put into each of theleft eyes. 90 minutes later, the lenses were removed, the eyes wereirrigated with saline and the corneal and anterior chamberconcentrations were determined. The lenses were then reinserted and therabbits received 1 drop of the 0.01%- solution in the left eye every 30minutes for 2 additional hours. Saline solution was instilled into theright eye. The corneal and aqueous humor concentrations of fluoresceinat 1 /2 and 3 /2 hours are shown in Tables 3 and 4 below. The ocularconcentrations attained with the pre-soaked lenses were 4 times higherthan those attained with frequent drops. Increasing the concentration ofthe soaking solution ten-fold resulted in an 800% increase in the ocularconcentrations. It took much less fluorescein to get TABLE 1.-CORNEALCONCENTRATION OF CEIN WITH DIFFERENT TYPES OF CONTACT LENSES IN PLACE[All values are X10 mg./ml.]

Bausch Methyl Present & Lomb methec Time (hours) lens lens rylate Nolens TABLE 2.-ANTERIOR CHAMBER CONCENTRATION OF LENSES IN PLACE [Allvalues are XlO- mg./ml.]

Bausch Methyl Present & Lomb methac- Time (hours) lens lens rylate Nolens TABLE 3.CORNEAL FLUORESCEIN CONCENTRATION IN RABBITS WITH PRESOAKEDLENSES OF PRESENT INVENTION [All values are XlO- mg./ml. (number ofanimals in parenthesis)] Lens presoaked ln- I TABLE 4.FLUO RESCEINCONCENTRATION IN AQUEOUS [All values are l0- mg./ml. (number of animalsin parenthesis)] Lens presoaked in- Topical Time (hours) fluoresceinfluorescein fluorescein OXYGEN PERMEABILITY STUDIES The lenses of thepresent invention appears to permit higher transmission of oxygen thanthe commercially available hydrophilic lens and, as a consequence, is ofvalue in permitting oxygen access across the lens to the cornea.

The lenses of the present invention, made by the twostage initiationprocess shown in FIG. 1 without the further steps of irradiation andhydrogen peroxide treatment, exhibit permeability and difiusioncharacteristics comparable to those pointed out in the studies above;and these lenses, cut from the polymerized rod, as shown in FIGS. 4a-4d,respond to hydrogen peroxide toughening and cleaning, although to adegree substantially less than the lenses which are made by thepreferred method of the invention as shown in FIG. 3.

The diffusibility of solutes through the lenses made by the methods ofFIGS. 1 and 3 is from about 6 to about 20 times as great as thediffusibility of the commercially available Sofiens, this ditfusibilitybeing expressed as the rate of elution of a dilute tracer materialthrough the lens. A comparative diffusion value is demonstrated where adye is seen to completely diffuse in a few hours through the lens of thepresent invention, while such diffusion through the presentlycommercially available lenses takes 24 hours or longer.

The significance of such diffusion is demonstrated when the novelcircular lens of our copending application, mentioned hereinabove, isplaced in contact with the cornea, over the super-sensitive limbal area,with its thin flap or edge extending a few millimeters beyond thelimbus, the

limbal area of the lens defining a circular tear vesiclewhich is cut outfrom the material of the lens adjacent the flap. This novel lens vesicleprovides a clear solution of liquid tears adjacent the cornea andosmotic pressure is created in a direction from the less dense tearliquid to the more dense liquid in the cornea to aid in bathing the eye.The semiscleral flap is held to the scleral portion of the eye bycapillary attraction. Tears can enter under the flap to replenish thevesicle well which is immediately adjacent the inner edge of the lens.Hypertonic eyedrops instilled into the eye stimulate the washing andcleaningfunction of the tears, and any medication in these eyedropsdiifuses rapidly, in mere minutes, through the permeable structure ofthe lens.

The hydrogen peroxide treatment appears not only to toughen the lens andraise the bursting strength values, as mentioned above, from 16 p.s.i.gauge to 19-20 p.s.i. gauge, but it also opens and cleans the pores ormicro voids in the lens material through which dilfusion takes place.Therefore, hydrogen peroxide at 3% dilution constitutes a maintenancefluid which is used in conjunction with 1% sodium bicarbonate solution,the latter relaxing the pores and softening the lens to aid in cleaningand reducing the bursting strength by 3 or 4 p.s.i. gauge units and theformer reversing this decrease to bring the lens back to its maximumtoughness after cleaning. Surprisingly, aging of the lens through normaluse, e.g. wearing and cleaning, has been found to slightly increase thebursting strength value of the lens by 2 or 3 p.s.i. gauge.

,Whether the lens is a newly manufactured lens having a burstingstrength of 16 p.s.i. gauge or an aged lens with bursting strength of 20p.s.i. gauge, no difference is found in the corrective function of thelens or in its comfort.

The lenses of the present invention resist the substantial dimensionalchanges which ordinarily occur when different osmotic saltconcentrations are applied. The anisotropic swelling and shrinkingcharacteristics at 50-55% water uptake appear to provide a uniqueevironment for resisting osmotic dimensional change which would causethe lens to shift its position or to flex in response to normal movementof the eyelid or illumination by strong light, irritation and the like.

If a lens is too stifi and insufficiently hydrated, which is the casewith the hydrophilic, highly cross-linked presently available commerciallens, the inside curve of the lens must be steeper than the curve of thecornea with a space under the lens in the central region in order toshape the lens to the cornea. It is this space which flexes with eachblink. The edge of the hydrophilic lens grabs the cornea at thesensitive limbal area. The inadequate water uptake causes irritation anddiscomfort. Only by increasing the lens diameter and by providing a verythin, flexible edge can the presently available commercial lens beimproved, but the liquid permeability is still insufficient and theoptical tolerance can never be as good as in the present lens becausethe present lens is cut in the hard state with a greater degree ofaccuracy than can be obtained with the prior art lens which is cut inthe soft state. Surprisingly, there is no dimensional change in thepresent lenses with small changes in hydration, while significantdimensional changes occur with the prior art lenses. Consequently, thefit is flatter and better with the present lens; the optical correctionis more accurate; substantially no shifting occurs; and flexing byblinking is completely avoided. In the present lens, the elimination offlexing, the smoother optical finish, the flatter corneal curve, and thelimbal tear vesicle make it possible to correct astigmatism in a mannerfar better than with any lens now available.

The chemical composition of the present hygroscopic lens, e.g. thecritical PVP and HEMA content, combined with the critical method oftwo-step polymerization to permit precision grinding and uniformity, andthe postpolymerization with radiation and hydrogen peroxide, provideprecision fitting, maximum strength, elasticity and l 14 elasticrecovery properties, all of which are essential to eye comfort when thelens is worn for long periods of time.

Instead of the polyvinyl pyrrolidone homopolymer, various lower alkylderivatives thereof may be employed. Such derivatives include:

3-methyI-Nvinyl-2-pyrrolidone 4-methyl-N-vinyl-2-pyrrolidone3,3-dimethyl-N-vinyl-2-pyrrolidone 4-ethyl-N-vinyl-Z-pyrrolidoneS-methyl-N-vinyl-2-pyrrolidone S-ethyl-N-vinyl-2-pyrrolidone and thelike. These examples support any PVP having lower alkyl in the 3, 4 or 5positions.

The composition also has utility as a liquid, hygroscopic coatingmaterial which strongly adheres to glass, plastic or metal when cured,after application, in two stages under the temperature conditions shownin FIG. 1. The liquid slurry can be applied in a thickness of 1-10 milsonto a glass tumbler to provide a frost-free drinking glass for colddrinks, the glass being free from outside condensation. The coating maybe applied to an automobile windshield to make it fog-free on theinside. The coating may be applied to the polycarbonate lenses used inski goggles or to contact lenses made of CR-39 (polycarbonate) plastic.

The membrane composition may be cast as a desalination membrane and usedto remove salt by reverse osmosis.

The membrane may be used as a germicide-carrying bandage for internaland external wounds, and in this aspect of the invention, our copendingapplication for Soft Plastic Bandage Containing Medicament forOphthalmic Use describes the inclusion of antibiotics, corticosteroids,antiseptics and disinfectants used in the chemotherapy of infectiousdiseases. In the treatment of the eye, these drugs include pilocarpine,belladonna alkaloids, dibenzyline, hydergine, methacholine, carbachol,bethanechol, and a sulfonamide and similar medicaments.

The precision fitting advantage of the lens of the present inventioncarries over to prevent liquid build-up behind the bandage when amedicament-carrying bandage is formed for the eyeball which extends overthe scleral area under the lid. Edema which is encountered with hard,impermeable acrylic bandages is eliminated. The medicines are notconcentrated in the present hydrated plastic membrane to cause osmoticswelling thereof, but are readily diflused to bathe the affected eyeportion with the proper concentrations for therapeutic elfectiveness.There is no dimensional change of the bandage when hypertonicconcentrations of salts and medicines are applied to the eye, and thisaids in the healing process.

The liquid slurry composition may be used to cast or coat an artificialeye, limb or appendage without shrinkage and to precise dimensions. Inall of these uses, the coating, membrane, casting, etc. can be cleanedwith hydrogen peroxide at an appropriate time.

Having thus disclosed the invention, what is claimed 1s:

1. An irradiated contact lens formed by cutting a hygroscopicpolymerized composition consisting essentially of 20-45% of a highmolecular weight and solid polyvinyl pyrrolidone and 55% ofmonomethacrylate ester of a glycol selected from the group consisting ofethylene glycol, propylene glycol, diethylene glycol and dipropyleneglycol, there being less than 1% methacrylic acid and 0.2%dimethacrylate impurities, initiated at 40-60 C. with a low temperaturefree-radical initiator selected from the group consisting of butylperoxide, di-secondary peroxy di-carbonate, and cyclohexanone peroxidefor 4-24 hours and further polymerized at -120 C. with a mediumfree-radical temperature initiator selected from the group consisting ofbenzoylperoxide, diethylperoxide, azoisobutyronitrile and orthotolylperoxide for A: to 2 hours, said lens being irradiated for from /2 to 4hours with 15 16 ultraviolet light in the spectral range of 2000-4000ang- 3,639,524 2/1972 Seiderman 260-885 stroms at a distance of thelight source up to 6 inches from 3,706,818 12/ 1972 Mageli et a1.260-885 the lens.

2. A contact lens as claimed in claim 1, which is swollen PAULLIEBERMAN, Primary Examiner with from 40-80% of water and treated withdilute hy- 5 PAGE, Assistant Examiner drogen peroxlde.

References Cited s CL XIR UNITED STATES PATENTS 204-15922; 260885;264-1; 351160 3,607,848 9/1971 Stoy etal 204159.l6

3,621,079 11/1971 Leeds 260885

